The invention relates to a method of recognizing a fault current in a control unit and to a control unit having a circuit for recognizing a fault current in a control unit.
Control units are known which are connected to a voltage supply and are supplied with input signals, the input signals supplied being used to switch on or switch at least one load connected to an output of the control unit. The load is arbitrary, so that pure resistive loads such as lamps can be involved here. Also, inductive and capacitive or other complex loads, such as solenoid valves, are conceivable as well.
To drive the load, the control unit comprises a driver which is actuated, for example, by a microprocessor integrated in the control unit and thus supplies a current to the load, which is connected to ground, for example. This means that, if the control unit and also the load are operating correctly, a current flows (depending on the polarity) from the control unit into the load, for example.
In incorrect operation, the current may not flow in the desired direction, but insteadxe2x80x94in the case just outlinedxe2x80x94a current may flow into the control unit, for example owing to a short circuit. This is undesirable because this fault current can cause damage to the control unit and its components or can cause the control unit to operate incorrectly.
To eliminate this problem, it is known to connect a diode in a series with the driver of the control unit, said diode being connected counter to the direction of the fault current and preventing the fault current from flowing. However, such a diode has the disadvantage that it becomes hot during operation of the control unit and the produces a high power loss, which is undesirable.
The invention is therefore based on the object of effectively detecting the occurrence of a fault current and of protecting the control unit against such a fault current without producing a power loss.
The invention proposes a method of recognizing a fault current in a control unit, in which a current flowing into the control unit via the output is detected and a fault signal is produced depending on the current detected. A fault current flowing into the control unit can be detected without any power loss, which does not impair the detection per se, so that the fault signal produced also brings about a fast reaction.
In a development of the invention, the load and/or the current supply for the control unit is switched off when the fault signal occurs. Hence, if a fault current flowing into the control unit has been detected in good time, this fault current can cause the load to be switched off so as to prevent further damage to the control unit, if the load is the fault source. If this is not the case (for example if there is a short circuit at the output and the load itself is operating correctly), the current supply for all the control units can also be switched off.
In addition or as an alternative, it is naturally also possible for the fault signal to be evaluated. Thus, for example, fault currents flowing briefly into the control unit, which, owing to their brevity, are not harmful, can be overlooked; if the fault currents are present for longer than a predefinable time interval, however, this is recognized as a fault situation and there is an appropriate reaction. Similarly, the level of the current flowing into the control unit can be detected and assessed. In this case, too, slight fault currents can be overlooked again, whereas fault currents above a predefinable magnitude cause a reaction and are evaluated to prevent damage to the control unit.